json.hpp - error: identifier '_json' preceded by whitespace in a literal operator declaration is deprecated - Ubuntu 25.04

[tomekit]

I've just upgraded from 24.04 to 25.04.

flutter build linux fails with:

/home/tom/data/Kapsa/flutter-drive/linux/flutter/ephemeral/.plugin_symlinks/flutter_secure_storage_linux/linux/include/json.hpp:24392:35: error: identifier '_json' preceded by whitespace in a literal operator declaration is deprecated [-Werror,-Wdeprecated-literal-operator]
/home/tom/data/Kapsa/flutter-drive/linux/flutter/ephemeral/.plugin_symlinks/flutter_secure_storage_linux/linux/include/json.hpp:24400:49: error: identifier '_json_pointer' preceded by whitespace in a literal operator declaration is deprecated [-Werror,-Wdeprecated-literal-operator]
/home/tom/data/Kapsa/flutter-drive/linux/flutter/ephemeral/.plugin_symlinks/flutter_secure_storage_linux/linux/include/json.hpp:24464:58: error: identifier '_json' preceded by whitespace in a literal operator declaration is deprecated [-Werror,-Wdeprecated-literal-operator]
/home/tom/data/Kapsa/flutter-drive/linux/flutter/ephemeral/.plugin_symlinks/flutter_secure_storage_linux/linux/include/json.hpp:24465:58: error: identifier '_json_pointer' preceded by whitespace in a literal operator declaration is deprecated [-Werror,-Wdeprecated-literal-operator]
Building Linux application...

I am not exactly sure if that this is causing the issue, but I've noticed that Ubuntu 25.04 runs now: libjsoncpp26 (previously libjsoncpp25) and newer: libjsoncpp-dev, current version 1.9.6-3, previously 1.9.5-6build1

I am not sure at this stage if I shall try to "force install" older version or perhaps there is some way to fix this issue.

Thanks for your help!

[tomekit]

It seems that libjsoncpp-dev version and libjsoncpp26 shouldn't be an issue, since this project includes NLohmann's JSON in the: flutter_secure_storage_linux/linux/include/json.hpp. Based on file header it uses version 3.11.2:

//     __ _____ _____ _____
//  __|  |   __|     |   | |  JSON for Modern C++
// |  |  |__   |  |  | | | |  version 3.11.2
// |_____|_____|_____|_|___|  https://github.com/nlohmann/json
//
// SPDX-FileCopyrightText: 2013-2022 Niels Lohmann <https://nlohmann.me>
// SPDX-License-Identifier: MIT

however when I've fetched the very exact version: https://github.com/nlohmann/json/tree/v3.11.2 (which BTW builds fine on my machine) I could find a lot of differences between the one that's included in flutter_secure_storage_linux, so I am not exactly sure what's going on.

Diff cmd:

meld /myflutterproject/linux/flutter/ephemeral/.plugin_symlinks/flutter_secure_storage_linux/linux/include/json.hpp /nlohmann.git/include/nlohmann/json.hpp

Anyway, if anyone could shed some light on this I would definitely appreciate that.

[tomekit]

As a temporary workaround I've added:

target_compile_options(${TARGET} PRIVATE -Wno-deprecated)

to Flutter project linux/CMakeLists.txt inside the function(APPLY_STANDARD_SETTINGS TARGET).

This allowed me to build project just fine, but probably isn't a long-term solution.

[ninoid]

As a temporary workaround I've added:

target_compile_options(${TARGET} PRIVATE -Wno-deprecated)

to Flutter project linux/CMakeLists.txt inside the function(APPLY_STANDARD_SETTINGS TARGET).

This allowed me to build project just fine, but probably isn't a long-term solution.

It works for me. Thanks!

[pugaizai]

only llvm20 will have this issue

[tmpfs]

Thanks a lot @tomekit this fixed the issue for me on arch :-)